Active matrix organic electroluminescent display device and method of fabricating the same

ABSTRACT

An organic electroluminescent display device includes a substrate, a gate line on the substrate, a data line crossing the gate line over the substrate, a switching thin film transistor near the crossing of the gate line and data line, a driving thin film transistor system including a plurality of sub-TFTs connected in parallel to the switching thin film transistor via a gate base, a power line crossing the gate line over the substrate and electrically connected with the plurality of sub-TFTs, a first electrode over the driving thin film transistor system in contact with the plurality of sub-TFTs, an organic electroluminescent layer on the first electrode, and a second electrode of transparent material on the organic electroluminescent layer.

The present invention claims the benefit of Korean Patent ApplicationNo. 2002-0088417 filed in Korea on Dec. 31, 2002, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and a method offabricating a display device, and more particularly, to an active matrixorganic electroluminescent display device and method of fabricating anactive matrix organic electroluminescent display device.

2. Discussion of the Related Art

An organic electroluminescent display device includes a cathodeelectrode to inject electrons, an anode electrode inject to holes, andan organic electroluminescent layer between the two electrodes. Anorganic electroluminescent diode has a multi-layer structure of organicthin films provided between the anode electrode and the cathodeelectrode. When a forward current is applied to the organicelectroluminescent diode, electron-hole pairs (often referred to asexcitons) combine in the organic electroluminescent layer as a result ofa P-N junction between the anode electrode, which injects holes, and thecathode electrode, which injects electrons. The electron-hole pairs havea lower energy when combined than when they were separated. Theresultant energy gap between the combined and separated electron-holepairs is converted into light by an organic electroluminescent element.In other words, the organic electroluminescent layer emits the energygenerated due to the recombination of electrons and holes in response toan applied current.

As a result of the above-described principles, the organicelectroluminescent device does not need an additional light source ascompared with a liquid crystal display device. Moreover, theelectroluminescent device is thin, light weight, and is very energyefficient. As a result, the organic electroluminescent device hasexcellent advantages when displaying images, such as a low powerconsumption, high brightness, and a short response time. Because ofthese advantageous characteristics, the organic electroluminescentdevice is regarded as a promising candidate for various next-generationconsumer electronic appliances, such as mobile communication devices,CNS (car navigation system), PDAs (personal digital assistances),camcorders, and palm PCs. Also, because the fabricating of such organicelectroluminescent devices is a relatively simple process, an organicelectroluminescent device is cheaper to produce than a liquid crystaldisplay device.

Organic electroluminescent display devices may be provided in either apassive matrix type arrangement or an active matrix type arrangement.The passive matrix type has a simple structure and fabrication process,but has a high power consumption as compared to the active matrix type.Further, because the display size of passive matrix organicelectroluminescent display devices is limited by its structure, thepassive matrix type can not easily be adapted to a large sized device.Moreover, the aperture ratio of the passive matrix type decreases as thebus lines increases. In contrast, active matrix type organicelectroluminescent display devices provide a higher display quality withhigher luminosity as compared to the passive matrix type.

FIG. 1 is a schematic cross-sectional view illustrating an active matrixtype organic electroluminescent display device according to a relatedart arrangement. As shown in FIG. 1, an organic electroluminescentdisplay device 10 includes first and second substrates 12 and 28, whichare attached to each other by a sealant 26. On the first substrate 12, aplurality of thin film transistors (TFTs) T and array portions 14 areformed. Each of the TFTs T corresponds to each pixel region P. A firstelectrode (i.e., an anode electrode) 16, an organic luminous layer 18and a second electrode (i.e., a cathode electrode) 20 are sequentiallyformed on the array portion 14. At this point, the organic luminouslayer 18 emits red (R), green (G) or blue (B) color in each pixel P. Inparticular, to show color images, organic color luminous patterns aredisposed respectively in each pixel P.

As additionally shown in FIG. 1, the second substrate 28, which isattached to the first substrate 12 by the sealant 26, includes amoisture absorbent 22 on the rear surface thereof. The moistureabsorbent 22 absorbs the moisture that may exist in the cell gap betweenthe first and second substrates 12 and 28. When disposing the moistureabsorbent 22 in the second substrate 28, a portion of the secondsubstrate 28 is etched to form a dent. Thereafter, a powder-typemoisture absorbent 22 is disposed into this dent, and then, a sealingtape 25 is put on the second substrate 28 to fix the powder-typemoisture absorbent 22 into the dent.

FIG. 2 is an equivalent circuit diagram illustrating a pixel of theorganic electroluminescent display device according to a related artarrangement. As shown in FIG. 2, a gate line GL is disposed in atransverse direction and a data line DL is disposed in a longitudinaldirection substantially perpendicular to the gate line GL. A switchingthin film transistor (switching TFT) T_(S) is disposed in a crossing ofthe gate and data lines GL and DL and a driving thin film transistor(driving TFT) T_(D) is disposed electrically connecting with theswitching thin film transistor T_(S). The driving TFT T_(D) iselectrically connected with an organic electroluminescent diode E. Astorage capacitor CST is disposed between a power line PL and a drain S6of the switching TFT T_(S). The storage capacitor CST is also connectedto a gate D2 of the driving TFT T_(D). A source S4 of the switching TFTT_(S) is connected to the data line DL, and a source D4 of the drivingTFT T_(D) is connected to the power line PL. The organicelectroluminescent diode E comprises a first electrode, an organicluminous layer and a second electrode, as described in FIG. 1. The firstelectrode of the organic electroluminescent diode E electricallycontacts with a drain D6 of the driving TFT T_(D), the organic luminouslayer is disposed on the first electrode, and the second electrode isdisposed on the organic luminous layer.

Now, an operation of the organic electroluminescent display device willbe briefly explained with reference to FIG. 2. When a gate signal isapplied to a gate S2 of the switching TFT T_(S) from the gate line GL, adata current signal flowing via the data line DL is converted into avoltage signal by the switching TFT T_(S) to be applied to the gate D2of the driving TFT T_(D). Thereafter, the driving TFT T_(D) is operatedand determines a current level that flows through the organicelectroluminescent diode E. As a result, the organic electroluminescentdiode E can display a gray scale between black and white.

The voltage signal is also applied to the storage capacitor CST suchthat a charge is stored in the storage capacitor CST. The charge storedin the storage capacitor CST maintains the voltage of the voltage signalon the gate S2 of the driving TFT T_(D). Thus, although the switchingTFT T_(S) is turned off, the current level flowing to the organicelectroluminescent diode E remains constant until the next voltagesignal is applied.

Meanwhile, the switching and driving TFTs T_(S) and T_(D) may includeeither of a polycrystalline silicon layer or an amorphous silicon layer.When the TFTs T_(S) and T_(D) include an amorphous silicon layer,fabrication of the TFTs T_(S) and T_(D) is more simple as compared toTFTs T_(S) and T_(D) that include a polycrystalline silicon layer.

FIG. 3 is a schematic plan view of an active matrix organicelectroluminescent display device having a bottom emission typeaccording to the related art. As shown in FIG. 3, the active matrixorganic light emitting diode device includes, for example, invertedstaggered type thin film transistors.

A gate line 36 crosses a data line 49 and a power line 62, which arespaced apart from each other. A pixel region is defined between the gateline 36 and the spaced apart data and power supply lines 49 and 62. Aswitching thin film transistor (TFT) T_(S) is disposed adjacent to wherethe gate line 36 and the data line 49 cross each other. A driving thinfilm transistor (TFT) T_(D) is disposed next to the power line 62 and inthe pixel region. The driving TFT T_(D) has a larger size than theswitching TFT T_(S), and therefore, the driving TFT T_(D) occupies arelatively large space of the pixel region.

The switching TFT T_(S) includes a switching gate electrode 32 extendingfrom the gate line 36, a switching source electrode 48 extending fromthe data line 49, a switching drain electrode 50 spaced apart from theswitching source electrode 48, and a switching active layer 56 a, abovethe switching gate electrode 32. The switching active layer 56 a, isformed of amorphous silicon and has an island shape.

The driving TFT T_(D) is connected to the switching TFT T_(S) and thepower line 62. The driving TFT T_(D) includes a driving gate electrode34, a driving source electrode 52, a driving drain electrode 54 and adriving active layer 58 a. The driving gate electrode 34 is connectedwith the switching drain electrode 50 and elongates along side the powerline 62. The driving active layer 58 a is formed of amorphous siliconand has a long island shape. Additionally, the driving active layer 58 aalso elongates along side the power line 62 while also overlapping thedriving gate electrode 34. The driving source and drain electrodes 52and 54 overlap side portions of the driving gate electrode 34. Thedriving active layer 58 a having an island shape is disposed above thedriving gate electrode 34 between the driving source and drainelectrodes 52 and 54.

As also shown in FIG. 3, the power line 62 has a protrusion extending tothe driving source electrode 50 and electrically communicates with thedriving source electrode 50 through the protrusion. A first electrode 66of the organic electroluminescent diode is disposed in the pixel regionand connected with the driving drain electrode 54.

The driving thin film transistor T_(D) needs to have an ability tooperate and drive the organic electroluminescent diode. Thus, a channelof the driving thin film transistor T_(D) should have a large channelwidth W and a short channel length L such that the ratio of width W andlength L should be large enough. Thus, the driving thin film transistorT_(D) can supply sufficient current to the organic electroluminescentdiode to operate and driving the organic electroluminescent diode.

FIGS. 4 and 5 are cross sectional views taken along lines IV-IV and V-Vof FIG. 3 illustrating the switching thin film transistor and thedriving thin film transistor, respectively.

In FIGS. 4 and 5, the switching gate electrode 32 and the driving gateelectrode 34 is formed on a substrate 30. Although not shown in FIGS. 4and 5, but shown in FIG. 3, the gate line 36 is also formed on thesubstrate 30. As described before, the driving gate electrode 34 islarger than the switching gate electrode 32 and occupies a large portionof the pixel region. A gate insulating layer 38 is formed on thesubstrate to cover the driving and switching gate electrodes 32 and 34and the gate line 36. The gate insulating layer 38 has a contact holethat exposes a bottom end of the driving gate electrode 34. A switchingsemiconductor layer 56 and a driving semiconductor layer 58 are formedon the gate insulating layer 38, respectively, above the switching gateelectrode 32 and above the driving gate electrode 34. The switchingsemiconductor layer 56 comprises a switching active layer 56 a, of pureamorphous silicon and a switching ohmic contact layer 56 b of dopedamorphous silicon. The driving semiconductor layer 58 is comprises adriving active layer 58 a of pure amorphous silicon and a driving ohmiccontact layer 58 b of doped amorphous silicon. As shown in FIG. 3, thedriving semiconductor layer 58 is larger than the switchingsemiconductor layer 56. The switching source and drain electrodes 48 an50 are formed spaced apart from each other and contact the switchingohmic contact layer 56 b, and the driving source and drain electrodes 52and 54 are formed spaced apart from each other in contact with thediving ohmic contact layer 58 b. The switching drain electrode 50 alsoelectrically contacts the driving gate electrode 34. The data line 49 isalso formed on the gate insulating layer 38 and disposed perpendicularlycrossing the gate line.36, as shown in FIGS. 3 and 4. Therefore, theswitching thin film transistor T_(S) and the driving thin filmtransistor T_(D) are complete.

A first passivation layer 60 is formed over an entire of the substrate30 to cover the switching thin film transistor T_(S) and the drivingthin film transistor T_(D). The first passivation layer 60 has a contacthole that exposes the driving source electrode 52. Then, the power line62 is formed on the first passivation layer 60 and contacts the drivingsource electrode 52 through the contact hole, as shown in FIG. 5. Thepower line 62 is spaced apart from the data line 49 and perpendicularlycrosses the gate line 36, as shown in FIG. 3, thereby defining the pixelregion with the gate and data lines 36 and 49. A second passivationlayer 64 is formed over an entire of the substrate 30 to cover the powerline 62. The first and second passivation layers 60 and 64 have acontact hole that exposes a portion of the driving source electrode 54through the contact hole. The first electrode 66 of the organicelectroluminescent diode is formed on the second passivation layer 64and electrically contacts the driving drain electrode 54. The firstelectrode 66 is disposed in the pixel region as shown in FIG. 3.

In the related art shown in FIGS. 3-5, the driving active layer 58 a hasa wide channel width and a short channel length, so that the drivingthin film transistor T_(D) occupies a large amount of the pixel region.Therefore, an aperture ratio the bottom emission type organicelectroluminescent display device is decreased. Further, since a largeamount of current flows through the driving thin film transistor T_(D),current stress may be caused in the driving thin film transistor T_(D),thereby damaging the driving thin film transistor T_(D). Especially,when the DC bias is continuously applied to the driving thin filmtransistor T_(D), the electrical properties of the driving thin filmtransistors T_(D) deteriorates and eventually malfunctions. Accordingly,the active matrix organic electroluminescent display device having theabove-mentioned driving thin film transistor may show an residual imagephenomenon, thereby causing bad display quality. Additionally, when thedriving thin film transistor is deteriorated and malfunctioned by theelectrical stress, a dot defect occurs in the pixel.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organicelectroluminescent device (OELD) device and a method of fabricating anOELD device that substantially obviates one or more of the problems dueto limitations and disadvantages of the related art.

An object of the present invention is to provide an active matrix OELDdevice having a driving thin film transistor arrangement in a pixel withdecreased electrical current stress.

Another object of the present invention is to provide OELD device havingimproved image resolution and high aperture ratio.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, an organicelectroluminescent display device comprising a substrate; a gate line onthe substrate; a data line crossing the gate line over the substrate; aswitching thin film transistor near the crossing of the gate line anddata line; a driving thin film transistor system including a pluralityof sub-TFTs connected in parallel to the switching thin film transistorvia a gate base; a power line crossing the gate line over the substrateand electrically connected with the plurality of sub-TFTs; a firstelectrode over the driving thin film transistor system in contact withthe plurality of sub-TFTs; an organic electroluminescent layer on thefirst electrode; and a second electrode of transparent material on theorganic electroluminescent layer.

In another aspect, a method of fabricating an organic electroluminescentdisplay device including pixels each having a pixel region, a switchingregion and a driving region, comprises forming a first metal layer on asubstrate; patterning the first metal layer to form a gate line, aswitching gate electrode in the switching region, a gate base in thepixel region, and plural driving gate electrodes in the driving region;forming a first insulating layer on the substrate to cover the gateline, the switching gate electrode, the gate base and the plural gateelectrodes; forming a switching active layer on the first insulatinglayer over the switching gate electrode and plural driving active layerson the first insulating layer over the plural driving gate electrodes;forming a second metal layer over the switching and driving activelayers; patterning the second metal layer to form a switching source, aswitching drain electrode, plural driving source electrodes, and pluraldriving drain electrodes, thereby forming a switching thin filmtransistor and a driving thin film transistor system, wherein thedriving thin film transistor system includes a plurality of sub-TFTseach having a corresponding driving gate electrode, a correspondingdriving active layer, a corresponding driving source electrode, and acorresponding driving drain electrode; forming a second insulating layerover the switching source and drain electrodes and the plural drivingdrain electrodes, wherein the second insulating layer has source contactholes the expose portions of the plural driving source electrodes;forming a power line on the second insulating layer, the power linedefining the pixel region with the gate and data lines and electricallycommunicating with the plural driving source electrodes through thesource contact holes; forming a third insulating layer on the secondinsulating layer on the second insulating layer to cover the power line,the third insulating layer having drain contact holes exposing theplural driving drain electrodes; forming a first electrode on the thirdinsulation layer within the pixel region, the first electrode contactingthe plural driving drain electrodes via the drain contact holes; formingan organic electroluminescent layer on the first electrode; and forminga second electrode of transparent material on the organicelectroluminescent layer.

In another aspect, an organic electroluminescent display devicecomprises a first substrate; a gate line on the first substrate; a dataline crossing the gate line over the first substrate; a switching thinfilm transistor near the crossing of the gate line and data line; adriving thin film transistor system including a plurality of sub-TFTsconnected in parallel to the switching thin film transistor via a gatebase; a power line crossing the gate line over the first substrate andelectrically connected with the plurality of sub-TFTs; an organicelectroluminescent diode on a second substrate; and a connection patternbetween the first and second substrates, the connection patternelectrically connecting the driving thin film transistor system to theorganic electroluminescent diode.

In another aspect, a method of fabricating an organic electroluminescentdisplay device including pixels each having a pixel region, a switchingregion and a driving region, comprises forming a first metal layer on afirst substrate; patterning the first metal layer to form a gate line, aswitching gate electrode in the switching region, a gate base in thepixel region, and plural driving gate electrodes in the driving region;forming a first insulating layer on the first substrate to cover thegate line, the switching gate electrode, the gate base and the pluralgate electrodes; forming a switching active layer on the firstinsulating layer over the switching gate electrode and plural drivingactive layers on the first insulating layer over the plural driving gateelectrodes; forming a second metal layer over the switching and drivingactive layers; patterning the second metal layer to form a switchingsource, a switching drain electrode, plural driving source electrodes,and plural driving drain electrodes, thereby forming a switching thinfilm transistor and a driving thin film transistor system, wherein thedriving thin film transistor system includes a plurality of sub-TFTseach having a corresponding driving gate electrode, a correspondingdriving active layer, a corresponding driving source electrode, and acorresponding driving drain electrode; forming a second insulating layerover the switching source and drain electrodes and the plural drivingdrain electrodes, wherein the second insulating layer has source contactholes the expose portions of the plural driving source electrodes;forming a power line on the second insulating layer, the power linedefining the pixel region with the gate and data lines and electricallycommunicating with the plural driving source electrodes through thesource contact holes; forming a third insulating layer on the secondinsulating layer on the second insulating layer to cover the power line,the third insulating layer having drain contact holes exposing theplural driving drain electrodes; forming a connection pattern on thethird insulating layer within the pixel region, the connection patterncontacting the plural driving drain electrodes via the drain contactholes; and forming an organic electroluminescent diode on a secondsubstrate, the connection pattern electrically connecting the drivingthin film transistor system to the organic electroluminescent diode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic cross-sectional view illustrating an active matrixtype organic electroluminescent display device according to a relatedart arrangement;

FIG. 2 is an equivalent circuit diagram illustrating a pixel of theorganic electroluminescent display device according to a related artarrangement;

FIG. 3 is a schematic plan view of an active matrix organicelectroluminescent display device having a bottom emission typeaccording to the related art;

FIGS. 4 and 5 are cross sectional views taken along lines IV-IV and V-Vof FIG. 3 illustrating the switching thin film transistor and thedriving thin film transistor, respectively;

FIG. 6 is a schematic plan view of an active matrix organicelectroluminescent display device according to the present invention;

FIGS. 7A-7E are cross sectional views taken along a line VII-VII of FIG.6 and illustrate an exemplary fabrication process for the active matrixorganic electroluminescent display device according to one exemplaryarrangement of the present invention; and

FIG. 8 is a cross sectional view of a dual panel type organicelectroluminescent display device according to another exemplaryarrangement of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, similar reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 6 is a schematic plan view of a pixel of an exemplary active matrixorganic electroluminescent display device according to the presentinvention. The active matrix organic electroluminescent display deviceof FIG. 6 is a top emission type unlike the related art of FIG. 3. Agate line 101 crosses a data line 115 and a power line 128, which arespaced apart from each other. A pixel region is defined between the gateline 101 and the spaced apart data and power supply lines 115 and 128. Aswitching thin film transistor (TFT) T_(S) is disposed adjacent to wherethe gate line 101 and the data line 115 cross each other. A driving thinfilm transistor (TFT) T_(D) is disposed in the pixel region between thedata line 115 and the power line 128. The driving TFT T_(D) in thisarrangement is a transistor system that comprises a plurality ofsub-TFT, for example, first to fourth sub-TFTs.

The switching TFT T_(S) includes a switching gate electrode 102extending from the gate line 101, a switching source electrode 116extending from the data line 115, a switching drain electrode 118 spacedapart from the switching source electrode 116, and a switching activelayer 108 above the switching gate electrode 102. The switching activelayer 108 is formed of amorphous silicon and has an island shape. Theswitching drain electrode 118 has a connection with a driving gate base104 that extends parallel with the data line 1 15 and used forconnecting gate electrodes of the plural sub-TFTs of the driving TFTT_(D).

The driving TFT T_(D) has, for example, first to fourth sub-TFTs T_(D1),T_(D2), T_(D3) and T_(D4), which are connected in parallel with eachother. The first to fourth sub-TFTs T_(D1), T_(D2), T_(D3) and T_(D4)have gate electrodes 104 a, 104 b, 104 c and 104 d, respectively, whichextend perpendicular from the driving gate base 104. The first to fourthsub-TFTs T_(D1), T_(D2), T_(D3) and T_(D4) have active layer 112 a, 112b, 112 c and 112 d, respectively, each of which is disposed above eachof the gate electrodes 104 a, 104 b, 104 c and 104 d. Additionally, thefirst to fourth sub-TFTs T_(D1), T_(D2), T_(D3) and T_(D4) includesource electrodes 120 a, 120 b, 120 c and 120 d and drain electrodes 122a, 122 b, 122 c and 122 d. The first source electrode 120 a is spacedapart from the first drain electrode 122 a across the gate electrode 104a, the second source electrode 120 b to the second drain electrode 122 bacross the second gate electrode 104 b, the third source electrode 120 cto the third drain electrode 122 c across the third gate electrode 104c, and the fourth source electrode 120 d to the drain electrode 122 dacross the fourth gate electrode 104 d. The first drain electrode 122 aand the second drain electrode 122 b are formed as one united body, thesecond source electrode 120 b and the third source electrode 120 c areformed as one united body, and the third drain electrode 122 c and thefourth drain electrode 122 d are formed as one united body. First tothird power electrodes 128 a, 128 b and 128 c extend from the power line128 over the driving TFT T_(D). The first power electrode 128 a overlapsand contacts the first source electrode 120 a, the second powerelectrode 128 b overlaps and contacts the one united body of the secondand third source electrodes 120 b and 120 c, and the third powerelectrode 128 c overlaps and contacts the fourth source electrode 120 d.First and second drain contact holes 132 a and 132 b are formed in themiddle of the united body of the first and second drain electrodes 122 aand 122 b and in the middle of the united body of the third and fourthdrain electrodes 122 c and 122 d. In this manner, the first and fourthTFTs T_(D1), T_(D2), T_(D3) and T_(D4), which are parallel connected,are complete. Although FIG. 6 shows the four sub-TFTs, the number ofsub-TFTs can increase (or decrease) using the above-mentionedconfiguration. Meanwhile, although not shown in FIG. 6, a firstelectrode of the organic electroluminescent diode electricallycommunicates with the drain electrodes 122 a, 122 b, 122 c and 122 d bycontacting them through the first and second drain contact hole 132 aand 132 b.

In the structure and configuration described with reference to FIG. 6,the driving TFT T_(D) includes the parallel-connected sub-TFTs T_(D1),T_(D2), T_(D3) and T_(D4), so that the driving TFT T_(D) alleviates anddistributes the overflowing electrical current stress. Furthermore,since the plural sub-TFTs exist and are used for driving the organicelectroluminescent diode, the driving TFT T_(D) can safely operate evenwhen one of the sub-TFTs is damaged.

FIGS. 7A-7E are cross sectional views taken along a line VII-VII of FIG.6 and illustrate an exemplary fabrication process for the active matrixorganic electroluminescent display device according to one exemplaryarrangement of the present invention.

In FIG. 7A, a substrate 100 having a switching region T_(S), a drivingregion T_(D) and a pixel region P is provided. Thereafter, a first metallayer is deposited on the substrate 100. The first metal layer may beformed of aluminum (Al), tungsten (W), copper (Cu), molybdenum (Mo),titanium (Ti), aluminum neodymium (AlNd) or alloys thereof. The firstmetal layer is then patterned to form a gate line (reference 101 of FIG.6), a switching gate electrode 102, a gate base 104 and first to fourthdriving gate electrodes 104 a-104 d. The switching gate electrode 102extends from the gate line and is disposed in the switching regionT_(S), while the first to fourth driving gate electrodes 104 a-104 dextend from the gate base 104 and are disposed in the driving regionT_(D). The gate base 104 is elongated perpendicular to the gate line anddisposed in the pixel region, as shown in FIG. 6. Additionally, the gatebase 104 connects the first and fourth driving gate electrodes 104 a-104d at the ends thereof.

After patterning the first metal layer, a gate insulating layer 106 isformed on the entire resultant surface of the substrate 100 to cover thegate line, the switching gate electrode 102, the gate base 104 and thefirst to fourth driving gate electrodes 104 a-104 d. The gate insulatinglayer 106 is preferably an inorganic material, for example, siliconnitride (SiN_(x)) or silicon oxide (SiO₂). Then, the gate insulatinglayer 106 is patterned to have a gate contact hole 107 that exposes oneend of the gate base 104.

In FIG. 7B, a pure amorphous silicon (a-Si:H) layer and a dopedamorphous (n⁺ a-Si:H) silicon layer are sequentially formed on the gateinsulating layer 106 and then patterned, thereby forming active layers108 and 112 a-112 d and ohmic contact layers 110 and 114 a-114 d on thegate insulating layer 106. Of course, other suitable materials may beused. However, the active layers are generally the pure amorphoussilicon, and include a switching active layer 108 and first to fourthdriving active layers 112 a-112 d. The ohmic contact layers aregenerally the doped amorphous silicon and include a driving ohmiccontact layer 110 and first to fourth driving ohmic contact layers 114a-114 d. The switching active and ohmic contact layers 108 and 110correspond to the switching gate electrode 102, the first driving activeand ohmic contact layers 112 a and 114 a to the first driving gateelectrode 104 a, the second driving active and ohmic contact layers 112b and 114 b to the second driving gate electrode 104 b, the thirddriving active and ohmic contact layers 112 c and 114 c to the thirddriving gate electrode 104 c, and the fourth driving active and ohmiccontact layers 112 d and 114 d to the fourth driving gate electrode 104d.

Thereafter, a second metal layer is formed over an entire resultantsurface of the gate insulating layer 106 to cover the active layers 108and 112 a-112 d and the ohmic contact layers 110 and 114 a-114 d, andthen patterned to form source electrodes 116 and 120 a-120 d and drainelectrodes 118 and 122 a-122 d. Each of the source electrodes 116 and120 a-120 d is spaced apart from the corresponding drain electrode. Theswitching source and drain electrodes 116 and 118 are formed on theswitching ohmic contact layer 110, and the switching drain electrode 118contacts the gate base 104 through the gate contact hole 107. The firstto fourth driving source and drain electrodes 120 a-120 d and 122 a-122d are formed on the first to fourth driving ohmic contact layers 114a-114 d, respectively. In the exemplary arrangement of present inventionas illustrated here, the first driving drain electrode 122 a has oneunited body with the second driving drain electrode 122 b. The seconddriving source electrode 120 b has a one united body with the thirddriving source electrode 120 c. The third driving drain electrode 122 chas a one united body with the fourth driving drain electrode 122 d.Although only four driving source and drain electrodes are shown in FIG.7B, more (or less) than four are possible in this manner. Additionally,each of the driving source and drain electrodes can be formedseparately.

After forming the source and drain electrodes described above, portionsof the ohmic contact layers 110 and 114 a-114 d exposed between thesource and drain electrodes are removed, thereby forming a channel onthe underlying active layers 108 and 112 a-112 d. Accordingly, a drivingTFT T_(D) having the parallel-connected sub-TFTs is complete, and aswitching TFT T_(S) has an electrical connection with the driving TFTT_(D) via the gate base 104 is complete.

Now in FIG. 7C, a first passivation layer 124 is formed over an entiresurface of the substrate 100 to cover the source electrodes 116 and 120a-120 d and the drain electrodes 118 and 122 a-122 d. Then, the firstpassivation layer 124 is patterned to expose portions of the drivingsource electrodes 120 a-120 d. A first source contact hole exposes thefirst driving source electrode 120 a, a second source contact holeexposes a middle portion between the second driving source electrode 120b and the third driving source electrode 120 c. After that, a thirdmetal layer is formed over an entire of the first passivation layer andthen patterned to form a power line (reference 128 of FIG. 6) as well asfirst and third power electrodes 128 a-128 c. As shown in FIG. 6, thepower electrodes 128 a-128 c extend from the power line over the drivingsource electrodes 120 a-120 d. The first power electrode 128 a contactsthe first driving source electrode 120 a through the first sourcecontact hole, and the second power electrode 128 b contacts the secondand third driving source electrodes 120 b and 120 c through the secondsource contact hole. Also, the third power electrode 128 c contacts thefourth driving source electrode 120 d through the third source contacthole.

In FIG. 7D, a second passivation layer 130 is formed over the firstpassivation layer 124 to cover the power line 128 and the powerelectrode 128 a-128 d. Then, the first and second passivation layers 124and 130 are simultaneously patterned to form first and second draincontact holes 132 a and 132 b. The first drain contact hole 132 aexposes a middle portion between the first and second driving drainelectrodes 122 a and 122 b, and the second drain contact hole 132 bexposes a middle portion between the third and fourth driving drainelectrodes 122 c and 122 d. The second passivation layer 130 may be anorganic material, such as benzocyclobutene (BCB) or acrylic resin. Afterthese steps, the substrate shown in FIG. 7D having the thin filmtransistors for use in an organic electroluminescent display device isfabricated.

FIG. 7E shows a step of forming an organic electroluminescent diode onthe substrate having the thin film transistors. A conductive materialhaving a low work function, such as aluminum (Al), magnesium (Mg),calcium (Ca) or lithium-fluorine/aluminum(LiF/Al), is deposited all overthe substrate 100, thereby forming a first electrode 134 (i.e., acathode electrode). The first electrode 134 is formed to be disposed inthe pixel region P contacting the first to fourth driving drainelectrodes 122 a-122 d through the first and second drain contact holes132 a and 132 b. Thereafter, an organic electroluminescent layer 136 isformed on the first electrode 134. Although the organicelectroluminescent layer 136 is depicted as a single layer in FIG. 7E,it can be multiple-layered. If organic electroluminescent layer 136 is amultiple layer, the organic electroluminescent layer 136 can include anelectron injection layer, an emission layer and a hole injection layerin a sequential order from the first electrode 134. A second electrode138 having a high work function, such as indium-tin-oxide (ITO), isformed on the organic electroluminescent layer 136. The second electrode138 is transparent and acts as a anode electrode, so that the organicelectroluminescent display device shown in FIG. 7E becomes a topemission type. Since the organic electroluminescent display devicefabricated through FIGS. 7A-7E is the top emission type, light isemitted along the direction opposite to the substrate where the linesand TFTs are disposed, thereby increasing the display area andsimplifying design the TFTs.

FIG. 8 is a cross sectional view of a dual panel type organicelectroluminescent display device according to another exemplaryarrangement of the present invention. Here, the organicelectroluminescent display device 99 has two substrates on which thethin film transistors and the organic electroluminescent diode arerespectively disposed.

In FIG. 8, first and second spaced apart substrates 100 and 200, whichhave inner surfaces facing each other, have a plurality of pixel regionsP. An array layer including switching and driving thin film transistors(TFTs) T in each pixel region is formed on an inner surface of the firstsubstrate 100. A connection pattern 400 connected to the TFT T is formedon the array layer in each pixel region. The connection pattern 400 canbe made of a conductive material or multiple layers, including aninsulating material with one or more layers of conductive material,having sufficient thickness for connection. An additional connectionelectrode can be used for connecting the connection pattern 400 and theTFT T. The TFT T includes the inventive driving TFT described withreference to FIGS. 6 and 7A-7E. The connection pattern 400 is connectedto the driving drain electrodes of the driving TFT having the pluralsub-TFTs.

A first electrode 202 is formed on an inner surface of the secondsubstrate 200. An organic electroluminescent (EL) layer 208 includingred (R), green (G) and blue (B) organic emission layers 208 aalternately disposed in each pixel region is formed on the firstelectrode 202. A second electrode 210 is formed on the organic EL layer208 in each pixel region P. The organic EL layer 208 can be formed of asingle layer or of multiple layers. In the case of multiple layers, theorganic EL layer 208 may include a first carrier-transporting layer 208b on the first electrode 202, one each of red (R), green (G) and blue(B) emission layers 208 a on the first carrier-transporting layer 208 b,and a second carrier-transporting layer 208 c on each of the emissionlayers 208 a. For example, when the first and second electrodes 202 and210 are respectively an anode and a cathode, the firstcarrier-transporting layer 208 b corresponds to a hole-injecting layerand a hole-transporting layer, and the second carrier-transporting layer208 c corresponds to an electron-transporting layer and anelectron-injecting layer. The first and second electrodes, 202 and 210,and the organic EL layer 208 interposed therebetween define an organicEL diode.

The first and second substrates 100 and 200 are attached with a sealant300 at a peripheral portion thereof. A top surface of the connectionpattern 400 contacts bottom surface of the second electrode 210, so thata current of the driving TFT T_(D) is flowing into the second electrode210 through the connection pattern 400. An organic electroluminescentdisplay device as described with reference to FIG. 8 is a dual paneltype where an array layer and an organic EL diode are formed onrespective substrates and where a connection pattern 400 electricallyconnects the array layer to the organic EL diode, which is an organicelectroluminescent diode. The TFTs T of FIG. 8 can be fabricated throughthe process described in FIGS. 7A-7E, and various modifications andvariations can be made in the structure of the TFTs and the connectingmethod of the array layer and the organic EL diode. Moreover, since theorganic electroluminescent display device of FIG. 8 is a top emissiontype, the thin film transistors T can be easily designed to obtain ahigh resolution and high aperture ratio.

Accordingly, the present invention has a number of advantages. Forexample, since the driving TFT has a wide channel width and a shortchannel length, the driving thin film transistor can efficiently operateand drive the organic electroluminescent diode. Further, although alarge amount of current flows through the driving thin film transistor,the current stress is prevented in the driving TFT because the drivingTFT has parallel-connected sub-TFTs. Therefore, the driving TFT is notdamaged. Further, even if one of the sub-TFTs is damaged andmalfunctioned, the driving TFT operable because the sub-TFTs areparallel connected. Since the organic electroluminescent display deviceis a top emission type, increased aperture ratio can be obtained.Accordingly, the organic electroluminescent display device according tothe present invention can have high resolution and excellent displayquality.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the organicelectroluminescent display device and method of fabricating an organicelectroluminescent display device of the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1-13. (canceled)
 14. A method of fabricating an organicelectroluminescent display device including pixels each having a pixelregion, a switching region and a driving region, the method comprising:forming a first metal layer on a substrate; patterning the first metallayer to form a gate line, a switching gate electrode in the switchingregion, a gate base in the pixel region, and plural driving gateelectrodes in the driving region; forming a first insulating layer onthe substrate to cover the gate line, the switching gate electrode, thegate base and the plural gate electrodes; forming a switching activelayer on the first insulating layer over the switching gate electrodeand plural driving active layers on the first insulating layer over theplural driving gate electrodes; forming a second metal layer over theswitching and driving active layers; patterning the second metal layerto form a switching source, a switching drain electrode, plural drivingsource electrodes, and plural driving drain electrodes, thereby forminga switching thin film transistor and a driving thin film transistorsystem, wherein the driving thin film transistor system includes aplurality of sub-TFTs each having a corresponding driving gateelectrode, a corresponding driving active layer, a corresponding drivingsource electrode, and a corresponding driving drain electrode; forming asecond insulating layer over the switching source and drain electrodesand the plural driving drain electrodes, wherein the second insulatinglayer has source contact holes the expose portions of the plural drivingsource electrodes; forming a power line on the second insulating layer,the power line defining the pixel region with the gate and data linesand electrically communicating with the plural driving source electrodesthrough the source contact holes; forming a third insulating layer onthe second insulating layer on the second insulating layer to cover thepower line, the third insulating layer having drain contact holesexposing the plural driving drain electrodes; forming a first electrodeon the third insulation layer within the pixel region, the firstelectrode contacting the plural driving drain electrodes via the draincontact holes; forming an organic electroluminescent layer on the firstelectrode; and forming a second electrode of transparent material on theorganic electroluminescent layer.
 15. The method according to claim 14,wherein the gate line is disposed in a first direction, wherein theswitching gate electrode extends from the gate line, wherein the gatebase is disposed in a second direction perpendicular to the gate line,and wherein the plural driving gate electrodes extend from the gatebase.
 16. The method according to claim 14, wherein forming the firstinsulating layer forms a gate contact hole that exposes one end of thegate base, and wherein the switching drain electrode contacts the gatebase through the gate contact hole.
 17. The method according to claim14, wherein forming the switching active layer includes forming aswitching ohmic contact layer on the switching active layer, and whereinthe switching source and drain electrodes are spaced apart from eachother and contact the switching ohmic contact layer.
 18. The methodaccording to claim 14, wherein forming the plural driving active layersincludes forming plural driving ohmic contact layers on the pluraldriving active layers, wherein each of the plural driving source anddrain electrodes contacts each the plural ohmic contact layers, andwherein each of the plural driving drain electrodes is spaced apart fromeach of the plural driving source electrodes.
 19. The method accordingto claim 14, wherein the drain contact holes penetrate both the secondand third insulating layers.
 20. The method according to claim 14,wherein the driving thin film transistor system includes first to fourthsub-TFTs includes first to fourth driving gate electrodes, first tofourth driving source electrodes, first to fourth driving drainelectrodes, and first to fourth active layers.
 21. The method accordingto claim 20, wherein the first to fourth driving gate electrodes areconnected to the gate base to electrically connect the driving thin filmtransistor system to the switching thin film transistor.
 22. The methodaccording to claim 20, wherein the first driving drain electrode and thesecond driving drain electrode include one united body.
 23. The methodaccording to claim 22, wherein the first electrode contacts a middle ofthe one united body of the first and second driving drain electrodes.24. The method according to claim 20, wherein the second driving sourceelectrode and the third driving source electrode include one unitedbody.
 25. The method according to claim 20, wherein the third drivingdrain electrode and the fourth driving drain electrode include oneunited body.
 26. The method according to claim 25, wherein the firstelectrode contacts a middle of the united body of the third and fourthdriving drain electrodes.
 27. The method according to claim 20, whereineach of the first to fourth driving drain electrodes is spaced apartfrom each of the first to fourth driving source electrodes.
 28. Themethod according to claim 24, wherein forming the power line includesforming power electrodes that extend from the power line over the firstto fourth driving source electrodes with an electrical connection withthe first to fourth source electrodes.
 29. The device according to claim28, wherein a first power electrode contacts the first driving sourceelectrode, wherein a second power electrode contacts a middle of theunited body of the second and third driving source electrodes, andwherein a third power electrode contacts the fourth driving sourceelectrode. 30-62. (canceled)